Segmented-Parallel-Beam Stationary Cardiac SPECT Abstract: The objective of this project is to develop a stationary cardiac SPECT (single photon emission computed tomography) system using a novel segmented parallel-hole collimator mounted on a large-area NaI(Tl) detector. This stationary SPECT system is inexpensive to build, motion-free, and able to acquire consistent SPECT. This system can obtain true dynamic SPECT images. A stationary gamma camera for cardiac SPECT has been developed by Spectrum Dynamics, called D- SPECT. There is no gantry rotation in D-SPECT; however, the detectors are continuously sweeping. Therefore, D-SPECT is not a truly stationary system. A genuine stationary cardiac SPECT system has been proposed jointly by UC San Francisco and Western Cardiology Associates. Their system is a modified three-detector SPECT system, mounted with three multi- pinhole collimators. They have successfully acquired cardiac SPECT images using this setup. GE has also developed a stationary, multi-pinhole dedicated cardiac SPECT system called Alcyone. Our proposed research is to replace the multi-pinhole collimators with our original-design segmented parallel-hole collimators. In a segmented parallel-hole collimator, the entire detection area is partitioned into many smaller sub-regions. The collimator holes in each segment point to the heart. Our motivation for replacing the pinhole technology by segmented parallel-hole technology is based on the following facts. The resolution/sensitivity trade-off for the pinhole is excellent (good resolution and good sensitivity), but only in small object (e.g., small animal) imaging when it is operating in the image magnifying mode. In large object (e.g., human) imaging when the pinhole is operating in the image-reducing mode or when image and object have the same size, the resolution/sensitivity trade-off is poor (poor resolution and poor sensitivity). In addition, the number of angular views is limited in a stationary system, thus, in order to obtain more view angles, the images cannot be magnified. In this situation, segmented parallel-hole collimation is able to provide better resolution and detection sensitivity than pinhole collimation. The proposed research will carefully study and compare the conventional rotational systems, the multi- pinhole systems, and segmented parallel-hole systems, and will verify our hypothesis: For human cardiac studies, the segmented parallel-hole system will outperform the multi-pinhole systems and the conventional rotational systems in terms of image resolution and detection sensitivity. Patient feasibility studies are also planned. After this research establishes a solid foundation for the segmented parallel-hole system using a common clinical SPECT camera, patient studies, dynamic imaging with temporally consistent projections, and motion correction techniques will be developed under a future R01 grant.